AIDS is a disease which is the ultimate result of infection with human immunodeficiency virus (HIV). Currently, there is no effective vaccine which can protect the human population from HIV infection, so the development of an efficacious HIV-vaccine is urgently required. Previously, HIV-1 particles exhaustively inactivated by chemical treatments, a vaccinia vector encoding the whole envelope protein (gp160) of HIV-1, and purified recombinant gp120 have been evaluated as candidate HIV vaccines. Although inactivated HIV-1 virus preparations elicited a T-cell-mediated Delayed-Type Hypersensitivity (DTH) reaction in humans, and vaccinia/gp160 and gp120 recombinant vaccine candidates induced virus neutralizing antibodies, none of these immunogens has been shown to be an efficacious human HIV vaccine (ref. 1--the literature references referred to herein are listed at the end of the specification).
The inventors' interest in HIV vaccinology is to develop synthetic HIV-1 peptides for incorporation into vaccines and consider that the vaccinia HIV-1-recombinant subunit used in conjunction with these HIV-1 peptide vaccines may lead to the elicitation of more effective immune responses against HIV-1. To design synthetic HIV vaccine candidates, immunogenic viral B-cell neutralization epitopes (BE) containing a high degree of conserved sequence between viral isolates are linked to functional T-helper cell determinant(s) (THD) to elicit a strong and long lasting cross-protective antibody response. In addition, HIV-specific cytotoxic T-lymphocyte (CTL) epitopes may be included in the synthetic constructions to elicit cell-mediated immunity to HIV infection.
A specific and preferential spatial relationship between certain T- and B-cell epitopes may be necessary for tandem epitopes to be efficiently processed and thereby rendered immunogenic. Thus, it is important to identify the appropriate T- and B-cell epitope sequences in HIV-1 proteins and assemble them in the optimal configuration so that both T- and B- cell memory can be elicited effectively and antibodies of the desired specificity produced. THDs have been found not to be universal and are immunologically functional only when presented in association with the appropriate Major Histocompatibility Complex (MHC) class II antigens. There is a characteristic hierarchy of T-cell epitope dominance. To develop an effective synthetic AIDS vaccine, it is therefore important to utilize the most potent THD of the various HIV-1 gp160, gag, pol and other gene products. Recent studies have indicated that the gag gene products may play a crucial role in eliciting an immune response against HIV infection. Thus, clinical progression of AIDS is associated with a reduction of circulatory antibodies to the gag p24 protein and antibodies raised against an immunodominant gag p17 peptide are capable of inhibiting HIV-1 infection in vitro (refs. 2, 3).
In our published International Patent Application WO 90/13564, there are described the identification and characterization of a T-cell epitope of the core protein, p24E of HIV-1 and the construction of synthetic chimeric peptides comprising the amino acid sequence of the T-cell epitope linked to an amino acid sequence of a B-cell epitope of an envelope or core protein of HIV-1. By linking the B-cell epitopes to the T-cell epitopes, an immune response to the B-cell epitope was induced, whereas no such response was observed when the B-cell epitope was not so linked. Data are presented in such published application with respect to the p24 T-cell epitope, BE3 epitope, ENV epitope-and V3A epitope, all derived from the HIV-1/LAV isolate, with and without linker sequences between the epitopes.
Specific constructs which are tested in the published WO specification are BE3 linked to the C-terminal end of p24E by direct coupling or to the N-terminal end of the p24E either by two proline residues or by direct coupling, ENV linked to the N-terminal end and linked to the C-terminal end of p24E in both cases by two proline residues, and V3A linked to the N-terminal end of p24 by two proline residues.
The V3A sequence tested in that publication (residues 308-327) of the variable loop of HIV-1 gp120 from HIV-1/LAV isolate was made immunogenic by linking the molecule to the N-terminus of p24E with a proline-proline linker.
It is known from U.S. Pat. No. 4,925,784 (Crowl) to provide by recombinant means a fusion protein comprising amino acids 15 to 512 from the gag protein and 44 to 140 of the env protein of the LAV isolate of HIV-I (HTLV-III), i.e., a polypeptide or protein containing 1093 amino acids, considerably longer than any synthetic peptide, which do not exceed 150 amino acids in length and generally are not more than 50 amino acids long. Such large molecule fusion proteins are described as being useful in diagnostic applications and vaccine materials.
The envelope glycoprotein (env) of human immunodeficiency virus (HIV) is highly variable between independent isolates and also sequential isolates from a single infected individual. The amino acid variability in env is concentrated into specific variable regions (mostly in the surface portion gp120 generated by the proteolytic maturation of the initial gp160 gene product), with other regions being less variable. However, the most variable regions often contain neutralizing epitopes so that the virus partially evades the host's immune response and establishes a persistent infection. This variability presents problems for diagnostic techniques based upon specific interactions, with separate or mixed reagents usually being employed to test samples for HIV-1. This variability also presents problems for any possible vaccine or immune therapy, since any suitable agent will have to give a response towards the many strains of HIV-1.
Thus, in generating an immune response in a host to a plurality of immunologically distinct HIV isolates, two problems exist. Firstly, any particular host in an outbred population will have a particular HLA haplotype and will thus differentially respond to a particular T-cell epitope. Secondly, antibodies may not recognize or neutralize a plurality of immunologically distinct HIV isolates and in particular HIV isolates that have been freshly harvested from patients as primary field isolates.
It would be advantageous to provide for the purposes of diagnosis, generation of immunological reagents, treatment and vaccination against HIV, synthetic peptides comprising T-cell epitopes to which a plurality of hosts will respond and B-cell epitopes from protein of different HIV isolates including primary field isolates.